Immediately obvious with the invention of the airplane was the importance of controlling movement in flight, as an uncontrollable airborne airplane will soon crash. Aviators soon settled on ailerons for roll control. An aileron is a hinged panel on the trailing edge of the wing, usually located at the outboard portion of the wing, which, when deflected downwardly, increases the lift of that wing, to roll or bank the airplane into a turn. At the same time, the aileron on the other wing is deflected upwardly, to decrease the lift on that wing and thus augment the rolling motion. The ailerons on the opposing wings of an airplane are typically mechanically coupled to one another. The configuration and application of the conventional aileron system has changed little, if at all, over more than nine decades since the first fixed-wing aircraft were produced.
One of the most objectionable features of conventional aileron application is a phenomenon known as “adverse yaw,” and virtually all existing fixed-wing aircraft suffer disadvantageous consequences associated with adverse yaw. When a turn is initiated with conventional ailerons, the nose of the airplane turns first in a direction opposite to that of the intended turn. This is usually compensated by using rudder deflection to “coordinate” the turn. The adverse yawing motion is a direct result of aileron application. While producing more lift to bank the airplane into a turn, the downwardly-deflected aileron also produces more drag, which acts momentarily to cause the airplane's nose to turn in the direction opposite to the intended turn. That is, when one wing is lifted relative to the other wing by operation of a conventional aileron to bank the airplane into a turn, that wing is also pulled back away from the turn relative to the wing on the other side, causing the nose initially to turn, or yaw, in the direction opposite to the turn. This effect becomes increasingly detrimental as the roll rate increases and/or airspeed decreases.
Adverse yaw produced by the conventional aileron can also contribute to spin entry. Instinctive application of conventional ailerons during attempted spin recovery can aggravate the spin condition. When spinning, an airplane is descending and turning in a tight spiral flight path. The conventional aileron is not effective in spin recovery. In a left hand spin, for instance, the left wing is down and toward the center of the spiral. Instinctively, many pilots are tempted to initiate right stick or control yoke movement to roll towards the right and out of the spin. With conventional ailerons this will deploy the left aileron down and the right aileron up. The left aileron may create more drag than the form drag caused by the up-going right aileron and the spin may be further aggravated. For an airplane equipped with conventional ailerons, application of rudder alone is used for spin recovery. Much of spin training involves conditioning pilots to avoid the instinctive attempt to roll out of the spin. Nonetheless, many pilots have aggravated spins by attempting such recoveries with conventional ailerons.
Various methods and devices have been used to counter adverse yaw. Among them are the differential aileron with its finite deflection ratio, and the spoiler. The differential variation of conventional ailerons is the most commonly used solution and provides some marginal improvement, but has limitations. For instance, conventional ailerons use a fixed-ratio linkage mechanism and are coupled to each other. This limits their ability to precisely counteract adverse yaw because the major causes of adverse yaw vary with lift.
Use of spoilers may obviate adverse yaw, but spoilers present their own problems. Spoilers are so named because they spoil or effectively eliminate lift. Ailerons deliver continuously variable changes in lift within their operational envelopes, whereas spoilers operate in a stepwise manner, being functionally either on or off, and thus are difficult to modulate between full and zero effect. Roll control is difficult to achieve with spoilers without complicated sub-systems or augmenting devices.
Therefore, there is a need for an improved airplane wing design that allows a pilot the ability to better counteract adverse yaw. Further, there is a need for an improved wing design that uses ailerons that can be controlled automatically. Further, there is also a need for an aileron system where the ailerons are not mechanically coupled to one another.